Method and apparatus for unambiguous topological determinancy in an unpowered stack configuration

ABSTRACT

A stack position determination circuit in a stackable repeater is disclosed that includes an input connector, an output connector, an initial pin driving circuit, and a pin rotating circuit. The input connector includes a plurality of input connector repeater stack position pins arranged in an hierarchical order so that each input connector repeater stack position pin corresponds to a possible physical position of the repeater in a stack of repeaters. An output connector includes a plurality of output connector repeater stack position pins arranged in an hierarchical order so that each output connector repeater stack position pin corresponds to a possible position of the repeater in a stack of repeaters. An initial pin driving circuit is connected to an initial pin in the input connector repeater stack position pin hierarchical order. The initial pin corresponds to a first position in the stack of repeaters and the initial pin driving circuit is responsive to an initial repeater signal. The initial repeater signal has a state that is indicative of whether the repeater is physically connected in the first position in the stack of repeaters. The pin rotating circuit is connected between the input connector and the output connector. The pin rotating circuit connects each of the plurality of input connector repeater stack position pins to a pin selected from the plurality of output connector repeater stack position pins such that the position of the selected output connector repeater pin is one position lower in the output repeater stack position pin hierarchical order than the corresponding position in the input repeater stack position pin hierarchical order of the input repeater stack position pin that is connected to the selected output repeater stack position pin.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of Ser. No. 08/964,601 filed Nov. 6,1997 now U.S. Pat. No. 6,101,169.

This application claims priority to U.S. Provisional Patent ApplicationNo. 60/058,611 filed Sep. 10, 1997 and U.S. Provisional PatentApplication No. 60/062,391 filed Oct. 7, 1997.

This application is related to co-pending U.S. patent application Ser.Nos. 08/965,479, U.S. Pat. No. 6,178,176, U.S. Ser. No. 08/965,330, U.S.Pat. No. 5,961,619, U.S. Ser. No. 08/964,602, U.S. Pat. No. 6,092,214,U.S. Ser. No. 08/965,320, U.S. Pat. No. 5,945,814, U.S. Ser. No.08/965,460 U.S. Pat. No. 6,108,312 and U.S. Ser. No. 08/965,323, U.S.Pat. No. 6,134,240 which are incorporated herein by reference for allpurposes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to methods and apparatuses forunambiguously determining the position of a Fast Ethernet repeater in arepeater stack. More specifically, the invention relates to methods andapparatuses for automatically determining the position of a repeater ina stack of repeaters. When repeaters are plugged into a stack using astack bus cable, the relative positions of the repeaters may bereconfigured or changed. The present invention enables repeaters in thestick to determine their positions relative to each other, even when oneor more of the repeaters are powered off. This information may be usedin a number of ways. For example, the information may be used to createan hierarchy of repeaters for the purpose of determining which repeateris to perform some special stack function such as providing themanagement module for the stack. Also, the information may be used topresent a more accurate display to a network manager that reflects allrepeaters in the stack, even those that are powered off.

2. Description of the Related Art

The growth of local-area networks (LANs) has been driven by theintroduction of Ethernet Technology as well as the availability ofpowerful, affordable personal computers and workstations. As a result,applications that once were possible only on mainframe computers are nowrunning on LANs. Network speed and availability are criticalrequirements. However, existing applications and a new generation ofmultimedia, groupware, imaging, and database products can tax a networkrunning at Ethernet's traditional speed of 10 megabytes per second(Mbps). Moreover, with more applications requiring faster LAN speeds foracceptable performance, network managers increasingly find thathigh-performance computation platforms and mission-critical applicationscan overwhelm a 10 Mbps network. Network managers therefore areincreasingly implementing high-speed LAN technology.

Fast Ethernet

For organizations with existing Ethernet installations, increasing thenetwork speed to 100 Mbps is preferable to investing in a completely newLAN technology. This user preference has driven the industry's decisionto specify a higher-speed Ethernet that operates at 100 Mbps. Thishigher-speed Ethernet is known as Fast Ethernet.

In July 1993, a group of networking companies joined to form the leastEthernet Alliance. The charter of the group was to draft the 802.3 u100BaseT specification (“802.3 specification”) of the Institute ofElectrical and Electronics Engineers (IEEE) and to accelerate marketacceptance of Fast Ethernet technology. The final IEEE 802.3specification was approved in June 1995. Among the other goals of theFast Ethernet Alliance are: to maintain the Ethernet transmissionprotocol Carrier Sense Multiple Access Collision Detection (CSMA/CD); toSupport popular cabling schemes; and to ensure that Fast Ethernettechnology will not require changes to the upper-layer protocols andsoftware that run on LAN workstations. For example, no changes arenecessary to Simple Network Management Protocol (SNMP) managementsoftware or Management Information Bases (MIBs) in order to implementEast Ethernet.

Other high-speed technologies, such as 100 VG-AnyLAN and AsynchronousTransfer Mode (ATM), achieve data rates in excess of 100 Mbps byimplementing different protocols that require translation when datamoves to and from 10BaseT. Protocol translation requires changing theframe, which often incurs higher latencies when passing through layer 2(data-link layer) LAN switches.

In many cases, organizations can upgrade to 100BaseT technology withoutreplacing existing wiring. Options for 100BaseT media are the same asthose for 10BaseT. They include shielded and unshielded twisted pair(STP and UTP) and fiber. The Media Independent Interface (MII) providesa single interface that can support external transceivers for any of the100BaseT physical sublayers.

CSMA/CD

Carrier sense-collision detection is widely used in LANs. Many vendorsuse this technique with Ethernet and the IEEE 802.3 specification. Acarrier sense LAN considers all stations as peers, the stations contendfor the use of the channel on an equal basis. Before transmitting, thestations monitor the channel to determine if the channel is active (thatis, if another station is sending data on the channel). If the channelis idle, any station with data to transmit can send its traffic onto thechannel. If the channel is occupied, the stations must defer to thestation using the channel.

FIG. 1 depicts a carrier sense-collision detection LAN. Network devices102, 104, 106, and 108 are attached to a network bus 110. Only onenetwork device at a time is allowed to broadcast over the bus, since ifmore than one device were to broadcast at the same time, the combinationof signals on the bus would likely not be intelligible. For example,assume network devices 102 and 104 want to transmit traffic. Networkdevice 108, however, is currently using the channel, so network devices102 and 104 must “listen” and defer to the signal from network device108 which is occupying the bus. When the bus goes idle, network devices102 and 104 can then attempt to acquire the bus to broadcast theirmessages.

Because network device 102's transmission requires time to propagate toother network devices, these other network devices might be unaware thatnetwork device 102's signal is on the channel. In this situation,network another device, such as device 104 or device 106, transmit itstraffic even if network device 102 had already seized the channel alterdetecting that the channel was idle. This problem is called thecollision window. The collision window is a factor of the propagationdelay of the signal and the distance between two competing stations.Propagation delay is the delay that occurs before a network device candetect that another network device is transmitting.

Each network device is capable of transmitting and listening to thechannel simultaneously. When two network device signals collide, theycreate voltage irregularities on the channel, which are sensed by thecolliding network devices. The network devices then turn off theirtransmission and, through an individually randomized wait period,attempt to seize the channel again. Randomized waiting decreases thechances of another collision because it is unlikely that the competingnetwork devices generate the same wait time.

It is important that the total propagation delay not exceed the amountof time that is required to send the smallest size data frame. Thisallows devices to discard data corrupted by collisions by simplydiscarding all partial frames. It is therefore not desirable for entireframes of data to be sent before a collision is detected. Carrier sensenetworks are usually implemented on short-distance LANs because thecollision window lengthens as the channel gets longer. Longer channelsprovide opportunity for the more collisions and can reduce through-putin the network. Generally, a long propagation delay coupled with shortframes and high data transfer rates give rise to a greater incidence ofcollisions. Longer frames can mitigate the effect of long delay, butthey reduce the opportunity for competing stations to acquire thechannel.

The IEEE 802.3 specification sets a standard minimum frame size of 64bytes (512 bits). Therefore, it order for a network to comply with thestandard, a station on the network must not be able to transmit 64 bytesof data before a collision is detected.

Although Fast Ethernet maintains CSMA/CD, the Ethernet transmissionprotocol, it reduces the transmission time for each bit by a factor of10. Thus, the Fast Ethernet packet speed increases tenfold, from 10 Mbpsto 100 Mbps. Date can move between Ethernet and Fast Ethernet withoutrequiring protocol translation or software changes, because FastEthernet maintains the 10BaseT error control functions as well as theframe format and length.

Repeaters

While some Ethernet applications connect numerous network devices to anetwork bus that is literally a cable connecting the network devices, itis often more desirable to connect network devices using a repeater orhub. It should be noted that in the following description the term “hub”and the term “repeater” are used interchangeably. The repeater managescollision detection for the network devices so that the network devicesneed only broadcast messages without detecting collisions. The repeaternotifies a network device when a collision occurs during its attempt totransmit. In addition, the repeater implements a star topology so thatmore devices can be included on the network without violating any cablelength restriction and so that many devices can be added or removed fromthe network efficiently.

An Ethernet repeater is a device that serves as a central station forplugging network devices included in an Ethernet network, hence the term“hub.” The Ethernet repeater receives messages from the network devicesthat are plugged into it and broadcasts (or “repeats”) the message toall of the other devices on the network along a network bus if nocollision is detected. The repeater monitors network traffic in itscollision domain and assumes the responsibility for collision detection.The network devices thus simply broadcast messages to the repeater anddo not need to first listen before sending messages. If the repeater hasalready assigned the network bus to a device, then it notifies thedevice that tried to broadcast that a collision has occurred so that thenetwork device may try again later. The amount of time that it takes forthe repeater to receive a data signal and repeat that data signal out toevery port on which the data signal is to be broadcast is referred to asthe latency of the repeater.

The 802.3 specification contains maximum latency requirements thatcannot be exceeded by a conforming repeater. The maximum permissiblelatency, combined with the requirements for maximum cable length andrestrictions on the number and type of other devices allowed within acollision domain, limits the amount of time that it takes to notify anetwork device that a collision has occurred, ensuring that the overall802.3 design criteria is met that all collisions are detected before acomplete 64 byte frame is transmitted. If the maximum permissiblelatency were exceeded by a repeater, then multiple devices in therepeater's collision domain on an 802.3 ethernet network might broadcastcomplete frames of data before being notified of a collision. Asdescribed above, the broadcast of complete frames when a collisionoccurs would defeat a scheme for discarding data associated withcollisions by simply discarding all partial frames.

Thus, minimizing the latency of a repeater is critical if the repeateris to be implemented on a network in accordance with the 802.3specification. The 100BaseT standard defines two classes of repeaters:Class I and Class II. At most, a collision domain can include one ClassI or two Class II repeaters. Including more than one repeater in asingle collision domain is sometimes referred to as cascading repeaters.Specifically, in order to conform to the Class II requirement, thelatency a repeater must be less than 46 bit times. It should be notedthat the standard is expressed in terms of bit times, or the amount ofdata that could be transmitted on the network during the latency period.

Network Flexibility

The Class II requirement, which allows more than one repeater to beincluded in a single collision domain, significantly adds flexibility tonetwork topology. Expanding the number of ports available on a networkmay be accomplished by simply adding a second repeater in the samecollision domain as a single existing repeater. No switch is required.By limiting the latency of the two repeaters, it is ensured thatcollisions can be detected and devices connected to different repeaterscan be notified of collisions in time to stop sending data before acomplete frame is broadcast.

Because networks tend to constantly change and expand with networkdevices being added, it would be highly advantageous if, in addition tothe Class II feature of allowing two repeaters in a collision domain, itwere also possible that each of the two Class II repeaters wereexpandable or stackable. Additional ports could be added to a firstrepeater stack that functions as one Class II repeater and then a secondstack could be included as a second Class II repeater. Thus,stackability combined with cascadability would provide even greaterflexibility for network expansion.

In such a network with stackable and cascadable repeaters, the topologyof the network may become confusing. It is important in such a changingnetwork to provide network management tools to aid in visualizing andmanaging the network. It would be useful if, to that end, a method couldbe provided for determining how many repeaters are in the stack andwhich repeater is in which position. In particular, it would be usefulif all the repeaters in the stack could be detected and their positionsin the stack determined regardless of whether or not some of therepeaters in the stack were powered off.

Prior art methods have started a binary number at the beginning of thestack and have provided a counter at each repeater that increments thenumber of repeaters. The problem with this approach is that it breaksdown when a repeater is turned off and could also give spurious resultsif repeaters are plugged or unplugged while powered on. In some priorart system, when a repeater is powered off or goes down, that repeateris removed from the network management display, even though it is stillpresent physically. This can cause confusion. What is needed is areliable way of determining the number and order of repeaters in astack.

SUMMARY OF THE INVENTION

Accordingly, the present invention enables repeaters in the stack todetermine their relative position to each other, even when one or moreof the repeaters are powered off. A wiring rotation that includes fourwires inside a stack bus cable that connects each of the repeaters inthe repeater stack is provided that spins an address bit as the stackbus cable extends from repeater to repeater along the stack.

It should be appreciated that the present invention can be implementedin numerous ways, including as a process, an apparatus, a system, adevice a method or a computer readable medium. Several inventiveembodiments of the present invention are described below.

In one embodiment, a stack position determination circuit in a stackablerepeater includes an input connector, an output connector, an initialpin driving circuit, and a pin rotating circuit. The input connectorincludes a plurality of input connector repeater stack position pinsarranged in an hierarchical order so that each input connector repeaterstack position pin corresponds to a possible physical position of therepeater in a stack of repeaters. An output connector includes aplurality of output connector repeater stack position pins arranged inan hierarchical order so that each output connector repeater stackposition pin corresponds to a possible position of the repeater in astack of repeaters. An initial pin driving circuit is connected to aninitial pin in the input connector repeater stack position pinhierarchical order. The initial pin corresponds to a first position inthe stack of repeaters and the initial pin driving circuit is responsiveto an initial repeater signal. The initial repeater signal has a statethat is indicative of whether the repeater is physically connected inthe first position in the stack of repeaters. The pin rotating circuitis connected between the input connector and the output connector. Thepin rotating circuit connects each of the plurality of input connectorrepeater stack position pins to a pin selected from the plurality ofoutput connector repeater stack position pins such that the position ofthe selected output connector repeater pin is one position lower in theoutput repeater stack position pin hierarchical order than thecorresponding position in the input repeater stack position pinhierarchical order of the input repeater stack position pin that isconnected to the selected output repeater stack position pin. Thus, theinitial pin driving circuit drives the initial pin in response to theinitial repeater signal and the signal on each input connector repeaterstack position pin is rotated to one position lower in the outputconnector position pin hierarchical order.

These and other features and advantages of the present invention will bepresented in more detail in the following specification of the inventionand the accompanying figures which illustrate by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be readily understood by the followingdetailed description in conjunction with the accompanying drawings,wherein like reference numerals designate like structural elements, andin which:

FIG. 1 is a block diagram illustrating a carrier sense-collisiondetection LAN.

FIG. 2 is a block diagram illustrating a repeater stack.

FIG. 3A is a schematic diagram illustrating four repeater stack positionpins.

FIG. 3B is a schematic diagram illustrating how the order of fourrepeater stack position pins is spun between an output connection socketof a repeater and an input connection socket of a repeater.

FIG. 4 is a schematic diagram illustrating how the first pin is drivenhigh for the top repeater in the stack bus using the top signal.

FIG. 5 illustrates a repeater stack display that may be created based oninformation received about the position of each repeater in a repeaterstack.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiment of theinvention. An example of the preferred embodiment is illustrated in theaccompanying drawings. While the invention will be described inconjunction with that preferred embodiment, it will be understood thatit is not intended to limit the invention to one preferred embodiment.On the contrary, it is intended to cover alternatives, modifications,and equivalents as may be included within the spirit and scope of theinvention as defined by the appended claims. In the followingdescription, numerous specific details are set forth in order to providea thorough understanding of the present invention. The present inventionmay be practiced without some or all of these specific details. In otherinstances, well known process operations have not been described indetail in order not to unnecessarily obscure the present invention.

In one embodiment, a group of stacked Fast Ethernet repeaters areconnected together with cables. This arrangement is particularlydesirable because different repeaters can be plugged, unplugged, orexchanged by simply plugging and unplugging the cables. In contrast, anarrangement where repeaters plug directly into one another offers lessconvenience and flexibility. When stacked repeater units arereconfigured by changing the order in which the cables are plugged,repeaters on the end of the repeater stack synchronous bus may be movedto the middle of the bus or vice versa. Certain repeaters in the stackalso may be powered on or off. A system administrator or networkmanagement software may desire or need to know the reconfigured topologyof the network. Accordingly, the present invention provides a method andapparatus for unambiguously determining the network topology.

FIG. 2 is a block diagram illustrating a repeater stack 200. Repeaterstack 200 includes a bottom repeater 202, two middle repeaters 204 and206, and a top repeater 208. Each of the repeaters in the repeater stackare connected to each other via a repeater stack bus that includes astack bus connection cable 212 connected between repeater 202 and 204, astack bus connection cable 214 connected between repeater 204 and 206,and a stack bus connection cable 216 connected between repeater 206 and208. Each of the repeaters includes an input connector and an outputconnector. The output connector of each repeater in the stack isconnected via the stack bus connection cable to the input connector ofthe repeater above it in the stack. It should be noted that in someembodiments the order of the repeater connectors may be changed. Infact, it is an important advantage of this arrangement that the stackcan be reconfigured and the repeaters reordered by simply plugging andunplugging the repeater bus cable.

At the bottom of the repeater stack, repeater 202 has no repeater buscable connected to its input connector. Likewise, the output connectorof repeater 208 at the top of the repeater stack is not connected.

A method of determining which repeaters are located on the ends, thatis, the top and bottom of a repeater stack is described in U.S. patentapplication Ser. No. 08/965,330 which was previously incorporated byreference for all purposes. A top signal that is high is generated inthe top repeater in the stack, which, in the embodiment describedherein, is arbitrarily considered to be the first repeater in therepeater stack. For all repeaters in the stack except the top repeater,the top signal is low. The top signal is used to designate the firstrepeater on a set of repeater stack position pins as is described below.It should be noted that a bottom signal is also generated for the bottomrepeater in that stack and that in other embodiments, the bottom signalis used to designate the first repeater on a set of repeater stackposition pins.

FIG. 3A is a schematic diagram illustrating four repeater stack positionpins including a first position pin 301, a second position pin 302, athird position pin 303, and a fourth position pin 304. Each position pinrepresents a position in the repeater stack. As is described below, thepins are spun or rotated inside the repeater between the repeater inputconnector and the repeater output connector. Although in the embodimentdescribed herein, the spin of the pins will be described as occurringinside each of the repeaters between the input connector and the outputconnector of the repeater, it should be recognized that the pins couldalso be spun by rotating the wires inside a stack bus connection cablethat connects the output connector of one repeater to the inputconnector of another repeater. Spinning the pins inside the repeaters ispreferred because it is generally less expensive to switch pins usingcircuitry on a printed circuit board than it is to change the wiring inthe stack bus cable.

FIG. 3B is a schematic diagram illustrating how the order of fourrepeater stack position pins is spun between an input connection socket310 of a repeater and an output connection socket 320 of a repeater. Inthe embodiment shown, the position of the pins is each advanced by oneposition between the input connector and the output connector. That is,the signal on the first pin of the input connector is routed to thesecond pin of the output connector; the signal on the second pin of theinput connector is routed to the third pin of the output connector; thesignal on the third pin of the input connector is routed to the fourthpin of the output connector; and the signal on the fourth pin of theinput connector is routed to the first pin of the output connector.Thus, whatever signal is on the input connector is shifted by one pin orbit. In different embodiments, the pins may be spun according todifferent schemes. When the above described scheme is used and when thefirst pin is caused to be high as is described below, then the positionof each repeater in the stack may be read by looking at which of therepeater stack position pins is high at the input connection socket ofthe repeater. In the embodiment shown, the high signal moves from thefirst pin of the top repeater to the second pin of the second repeaterto the third pin of the third repeater to the fourth pin of the fourthrepeater. Thus, the pin number of the high pin corresponds to theposition of the repeater in the stack, numbered from the top.

FIG. 4 is a schematic diagram illustrating how the first pin is drivenhigh for the top repeater in the stack bus using the top signal. In eachrepeater an initial pin driving circuit 400 is implemented. A 5Vpotential is preferably provided from the stack bus connection cable. Inone embodiment the termination power pin is used as is described in U.S.patent applications Ser. Nos. 08/965,330 and 08/965,320 which werepreviously incorporated by reference for all purposes. The advantage ofusing the termination power pin is that power is available so long asone of the repeaters on the stack is powered on. On each repeater, afirst repeater stack position pin is softly pulled down to ground via apull down resistor 404. The first repeater stack position pin is alsoconnected to the 5V potential through an MOS switch 406. When the topsignal is high, then MOS switch 406 is closed and the first repeaterstack position pin is pulled high. When the top signal is low, the firstrepeater stack position pin stays low. Thus, the first repeater stackposition pin is pulled high for the top repeater in the repeater stack.

As pointed out above, the position of each repeater in the stack may bedetermined by which of the repeater stack position pins is high at theinput connection socket of the repeater. In other embodiments, therepeater stack position may be determined by which of the repeater stackposition pins is high at the output connection socket of the repeater.

In one embodiment, the position of each repeater in the stack isreported to a network management module either directly over the stackbus cable or via a network management module bus connecting networkmanagement modules. A display is then generated indicating the positionsof repeaters in the stack and, preferably the status of each repeater.FIG. 5 illustrates a repeater stack display that may be created based oninformation received about the position of each repeater in a repeaterstack. A bottom repeater 502 is graphically depicted next to a messageindicating that the repeater is on. Alternatively, bottom repeater maybe lit up to show that it is on and dimmed to indicate that it is off orflashing to indicate that a problem has occurred. A second repeater 504in the stack is graphically depicted next to a message indicating thatthe repeater is off. The depiction of a repeater that is off isspecifically made possible by the wiring scheme disclosed above.Finally, a third repeater is graphically depicted on top of the stacknext to a message indicating that it is on. A no repeater message 508indicates that there is not a fourth repeater in the stack.

In one embodiment, the position of each repeater in the stack is alsoused to determine the place in a network management module hierarchy ofa network management module plugged into a repeater for the purpose ofselecting primary and backup network management modules as is disclosedin U.S. patent application Ser. No. 08/964,602 which was previouslyincorporated by reference for all purposes.

A wiring rotation scheme has been disclosed for unambiguouslydetermining the topology of an unpowered repeater stack configuration.

Although the foregoing invention has been described in some detail forpurposes of clarity of understanding it will be apparent that certainchanges and modifications may be practiced within the scope of theappended claims. It should be noted that there are may alternative waysof implementing both the process and apparatus of the present invention.Accordingly, the present embodiments are to be considered asillustrative and not restrictive, and the invention is not to be limitedto the details given herein, but may be modified within the scope andequivalents of the appended claims.

What is claimed is:
 1. A circuit for determining the position of astackable repeater within a repeater stack, comprising: an inputconnector including a plurality of input pins, each input pincorresponding to a position within the repeater stack, the plurality ofinput pins including an initial pin corresponding to a first position inthe repeater stack; an output connector including a plurality of outputpins, each output pin corresponding to a position within the repeaterstack; an initial pin driving circuit connected to the initial pinwherein the initial pin driving circuit is configured to apply to theinitial pin a signal that is indicative of whether the repeater isconnected in the first position in the repeater stack; and a pinrotating circuit connected between the input connector and the outputconnector, wherein the pin rotating circuit connects each of theplurality of input pins to the output pin corresponding to the nextrepeater stack position; wherein the respective signals on the inputpins of the input connector indicate the position of the repeater in therepeater stack.
 2. The circuit of claim 1, wherein: the output pins areconnected to the corresponding input pins of a second input connectorassociated with a next repeater in the repeater stack; and therespective signals on the output pins indicate the position in therepeater stack of the next repeater.
 3. The circuit of claim 1, whereinthe initial pin driving circuit is responsive to an initial repeatersignal, the initial repeater signal having a state that is indicative ofwhether the repeater is physically connected in the first position inthe stack of repeaters.
 4. A circuit for determining the position of astackable repeater within a repeater stack, comprising: an inputconnector including a plurality of input pins, each input pincorresponding to a position within the repeater stack, the plurality ofinput pins including an initial pin corresponding to a first position inthe repeater stack; an output connector including a plurality of outputpins, each output pin corresponding to a position within the repeaterstack; an initial pin driving circuit connected to the initial pinwherein the initial pin driving circuit is configured to apply to theinitial pin a signal that is indicative of whether the repeater isconnected in the first position in the repeater stack; and a pinrotating circuit connected between the input connector and the outputconnector, wherein the pin rotating circuit connects each of theplurality of input pins to the output pin corresponding to the nextrepeater stack position; wherein the respective signals on the outputpins of the output connector indicate the position of the repeater inthe repeater stack.
 5. A circuit for determining the position of astackable repeater within a repeater stack, comprising: a plurality ofrepeaters, each of said repeaters comprising: an input connectorincluding a plurality of input pins, each input pin corresponding to aposition within the repeater stack, the plurality of input pinsincluding an initial pin corresponding to a first position in therepeater stack; an output connector including a plurality of outputpins, each output pin corresponding to a position within the repeaterstack; and an initial pin driving circuit connected to the initial pinwherein the initial pin driving circuit is configured to apply to theinitial pin a signal that is indicative of whether the repeater isconnected in the first position in the repeater stack; and a stack buscable connecting the output connector of a first one of said pluralityof repeaters with the input connector of a second one of said pluralityof repeaters, the stack bus cable is configured to connect each of theplurality of output pins to the input pin corresponding to the nextrepeater stack position; wherein the respective signals on the inputpins of the input connector of each of said plurality of repeatersindicate the position of the repeater in the repeater stack.
 6. A stackposition determination circuit in a stackable repeater comprising: meansfor receiving an input signal indicative of the position of thestackable repeater in the repeater stack; means for providing an outputsignal to a next repeater connected in a position that follows thestackable repeater in the repeater stack; means for generating a firstposition signal indicative of whether the stackable repeater isphysically connected in the first position in the stack of repeaters,said means for generating including means for causing said firstposition signal to be reflected in said input signal; and means forderiving the output signal from the input signal such that the outputsignal is indicative of the position in the repeater stack of the nextrepeater.
 7. A method of unambiguously determining the topology of arepeater stack comprising: a step for generating a first repeater stackposition signal in a first repeater that occupies a first position inthe repeater stack; a step for deriving from the first repeater stackposition signal an output signal indicative of the physical position ofa second repeater that occupies a second position in the repeater stack;and a step for providing the output signal to the second repeater;whereby the first repeater stack position signal reflects the positionin the repeater stack of the first repeater and the output signalreflects the position in the repeater stack of the second repeaterregardless of whether the first repeater and the second repeater arepowered on.